Fiber optic systems play an increasingly important role in transmission of signals. A common application uses WDM to combine many independent optical signals of different wavelengths onto one optical fiber for long distance transmission. Signals are routed through the network by demultiplexing signals from a group of input fibers into an individual fiber for each signal, directing the signals using a large cross-connect switch, then recombining the signals using wavelength multiplexers onto a group of output fibers.
Since excessively strong optical signals saturate optical amplifiers and reduce the gain available to weaker signals, desired signal to noise ratio is maintained in the network by keeping the optical power at each wavelength approximately the same. Consequently, loss at each wavelength must be carefully controlled across the network.
It is known that loss can be controlled by using programmable optical attenuators before or after the optical switch at the point where each optical signal is separate. However, these programmable optical attenuators add substantial cost, complexity and loss to the network. See “Optical Cross-Connect System In Broadband Networks: System Concept And Demonstrators Description”, Journal of Lightwave Technology, Vol. 11 (No. 5–6), May–June 1993, pp. 688–694, Johansson, S.; Lindblom, M.; Granestrand, P.; Lagerstrom, B.; Thylen, L.
An acousto-optic tunable filter (AOTF) can also be used in an optical network to equalize power levels as disclosed in, “MOSAIC: A Multiwavelength Optical Subcarrier Multiplexing Controlled Network”, IEEE Journal on Selected Areas in Communications, Special Issue on High Capacity Optical Networks, 16 (7), 1270–1285 (September 1998), Gaudino, R.; Len, M; Desa, G.; Shell, M.; Blumenthal, D. J.
An alternate method of balancing optical power in an optical network by detuning an optical switch in order to equalize optical loss or optical power was disclosed in pending U.S. patent application Ser. No. 09/855,765, “Wavelength Power Equalization by Attenuation in an Optical Switch”, which has issued as U.S. Pat. No. 6,697,547 B2. Balancing optical power is obtained by detuning one or more mirror electrodes in a MEMS-based switch using mirrors that rotate in two axes.